Coming back from Thunder, all I have on the brain are Mitchell's, so I started to wonder?
What if you had a B-25J, and you wanted to back date it to a D or C? What changes you would need to make to the J in order for it to be exact?, And who would you have do this?
My only guess would be Aero Trader. Of course this is providing that you didnt have enough money to buy that B model , or King 9.